You'll want to plant the grasses so they are at the same soil level they were growing before. Look at the stems and you should be able to tell how deep they were planted by finding soil stains around the stem. The roots of these plants are fiberous and can be draped along a trench. Try to dig a shallow hole that's long and probably only 3-4 inches deep. Lay the roots along the trench and fill in the soil (holding the top upright so it stays up) and then firm the soil by pressing it down with your hands. It doesn't have to be tight and solid, just firm enough to keep the tops of the plants upright. Water well after transplanting. Best wishes with your grasses!